For many years, polyethylene pillow-shaped bags have been used for packaging granular products, such as frozen vegetables. These bags must be stacked vertically because they do not stand up. When stacked vertically, it is difficult for a consumer to determine the contents because the principal display panel is concealed.
It is desirable to have bags which stand up so that the principal display panel faces the consumers. Arranging the bags in the standing up position also takes less supermarket shelf space. Stand-up bags for food products in some instances include pouring spouts. For example, U.S. Pat. No. 5,547,284 to Imer shows a stand-up bag having a corner portion which may be cut away to form a spout for pouring. U.S. Pat. No. 5,636,925 to Smiley shows a radially disposed perforation in the upper right hand corner of the bag to provide a pouring spout. In addition, the Smiley patent includes a handle located on top of the bag. U.S. Pat. No. 4,454,979 to Ikeda shows a bag which includes a handle that is cut away to form a spout for pouring. None of the known bags, however, are standup bags manufactured from an extruded heat sealable film which includes both an integral handle and a perforated section that can be torn to open the bag and form a pouring spout.
It is known to manufacture bags from coextruded polyethylene film or laminated film. The manufacturing process includes the step of sealing a bag by applying enough heat to the surface of the bag to melt the material and cause it to adhere to itself.
In order to heat seal bags manufactured from coextruded polyethylene, the packaging industry has developed a heat sealing mechanism that is similar in design to a light bulb filament. This heat seal mechanism generates enough heat to reach the melting point of the material. Only the inside layer needs to melt to create the seal. The remaining outer layers must be cooled so that they do not melt and cause the bag to lose its shape. The mechanism used for cooling may include blasts of cold air following the application of heat. The cooling step increases the time to produce bags manufactured from coextruded polyethylene. Thus, the bags can be produced at a rate of only about 60 bags per minute.
To avoid the manufacturing problems associated with heat sealing coextruded polyethylene, the packaging industry has used laminated film. Laminated film consists of layers of different material which are brought together. The layers may consist of such materials as polyethylene, polyester, paper, foil and polypropylene. The outside layer of laminated film consists of a heat resistant material, such as polyester, or is coated with heat resistant material. In either case, the outside layer melts at a higher temperature than the inside layer. This difference in melting points allows for the continuous application of high temperature jaws or some other suitable mechanism to the outer layer to effectuate a heat seal. The high temperature jaws, which can be set to a temperature higher than the melting point of the inside layer and lower than the melting point of the outer layer, melt the inside layer without melting the outer layer. A heat seal of the inside layer results without structural breakdown of the outer layer and eliminates the need for cooling the outer layer. The use of laminated film and high temperature jaws streamlines the manufacturing process and permits bags to be produced at a rate of about 90 bags per minute. However, the laminated film is approximately three times the cost of coextruded polyethylene.
Therefore, there is a need in the packaging industry to combine the cost advantages of using low cost extruded polyethylene film with the manufacturing advantages of using high temperature jaws in a continuous laminated film line, especially to create a standup bag for food or other granular products.